Conventionally, in the manufacture of semiconductor devices, micro-processing by lithography using a photoresist composition has been carried out. The micro-processing is a processing method including forming a thin film of a photoresist composition on a silicon wafer, irradiating actinic rays such as ultraviolet rays through a mask pattern depicting a pattern for a semiconductor device, developing it to obtain a resist pattern, and etching the silicon wafer using the resist pattern as a protective film. However, in recent progress in high integration of semiconductor devices, there has been a tendency that shorter wavelength actinic rays are being used, i.e., ArF excimer laser beam (wavelength 193 nm) have been taking the place of i-line (wavelength 365 nm) or KrF excimer laser beam (wavelength 248 nm). Along with this change, influences of random reflection and standing wave off a substrate have become serious problems. Accordingly, it has been widely studied to provide an anti-reflective coating between the photoresist and the substrate (Bottom Anti-Reflective Coating, BARC). In addition, it comes to be considered to utilize F2 excimer laser (wavelength 157 nm) being a light source with a shorter wavelength for micro-processing by lithography.
As the anti-reflective coating, inorganic anti-reflective coatings made of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon or α-silicon and organic anti-reflective coatings made of a light-absorbing substance and a polymer compound are known. The former requires an installation such as a vacuum deposition apparatus, a CVD (chemical vapor deposition) apparatus or a sputtering apparatus. In contrast, the latter is considered advantageous in that it requires no special installation so that many studies have been made. For example, mention may be made of the acrylic resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule and the novolak resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule (see, for example U.S. Pat. Nos. 5,919,599 and 5,693,691).
The physical properties desired for organic anti-reflective coating materials include high absorbance to light and radioactive rays, no intermixing with the photoresist layer (being insoluble in photoresist solvents), no diffusion of low molecular substances from the anti-reflective coating material into the topcoat resist upon coating or heat-drying, and a higher dry etching rate than the photoresist (see, for example, Tom Lynch et al., “Properties and Performance of Near UV Reflectivity Control Layers”, US, in Advances in Resist Technology and Processing XI, Omkaram Nalamasu ed., Proceedings of SPIE, 1994, Vol. 2195, p. 225-229; G. Taylor et al., “Methacrylate Resist and Antireflective Coatings for 193 nm Lithography”, US, in Microlithography 1999: in Advances in Resist Technology and Processing XVI, Will Conley ed., Proceedings of SPIE, 1999, Vol. 3678, p. 174-185; and Jim D. Meador et al., “Recent Progress in 193 nm Antireflective Coatings, US, in Microlithography 1999: in Advances in Resist Technology and Processing XVI, Will Conley ed., Proceedings of SPIE, 1999, Vol. 3678, p. 800-809).
By the way, a hitherto technique of anti-reflective coatings has been mainly considered on lithography process with irradiation light having a wavelength of 365 nm, 248 nm or 193 nm. As a result of such consideration, light absorbing components and light absorbing groups effectively absorbing light of each wavelength are developed, and they come to be utilized as one component of an organic anti-reflective coating composition. For example, it is known that chalcone dies prepared by condensation of 4-hydroxyacetophenone with 4-methoxybenzaldehyde are effective for irradiation light having a wavelength of 365 nm (see, for example Japanese Patent Laid-open No. Hei 11-511194), it is known that naphthalene group-containing polymers having a specific structure have high absorbance for irradiation light having a wavelength of 248 nm (see, for example Japanese Patent Laid-open No. Hei 10-186671), and it is known that resin binder compositions containing phenyl unit are excellent for irradiation light having a wavelength of 193 nm (see, for example Japanese Patent Laid-open No. 2000-187331).
In recent years, lithography process with F2 excimer laser (wavelength 157 nm) being a light source having a shorter wavelength comes to be regarded as next-generation technology in place of that with ArF excimer laser (wavelength 193 nm). It is considered that the former process permits micro-processing of process dimension not more than 100 nm, and at present its development and research have been actively carried out from the aspects of apparatus and material, etc. However, most of the research on material relate to photoresist, and it is an actual condition that the research on organic anti-reflective coatings is little known. This is because components effectively absorbing light having a wavelength of 157 nm, that is light absorbing components having a strong absorption band at 157 nm are little known.
It is considered that as irradiation light provides process dimension not more than 100 nm. Therefore, it is also considered that a photoresist is used in a form of thin film having a thickness of 100 to 300 nm that is thinner compared with the prior one. Organic anti-reflective coatings used along with such a photoresist in a form of thin film require the followings: they can be used in a form of a thin film; and they have a high selectivity of dry etching for photoresist. And, it is considered that organic anti-reflective coatings are required to have a large attenuation coefficient k so that they could be used in a shape of thin film having a thickness of 30 to 80 nm. In a simulation with PROLITH ver. 5 (manufactured by Litho Tech Japan; expected and ideal values are used as optical constants (refractive index, attenuation coefficient) of the photoresist), an anti-reflective coating having a base substrate made of silicon with a thickness of 30 to 80 nm can have second minimum thickness (about 70 nm), and in this case the coating has an attenuation coefficient k of 0.3 to 0.6 and a reflectance from substrate of 2% or less, thus has a sufficient anti-reflective effect. In addition, a similar simulation in which silicon oxide is used as base substance and a thickness of silicon oxide varies between 100 nm and 200 nm results in that attenuation coefficient k of 0.4 to 0.6 is required in order to exert a sufficient anti-reflective effect with an anti-reflective coating having a thickness of 70 nm. For example, in case where attenuation coefficient k is 0.2, reflectance from substrate varies between 5% and 10%, and in case where attenuation coefficient k is 0.4, reflectance from substrate varies between 0% and 5%. Consequently, it is considered that in order to exert a sufficient anti-reflective effect, a high attenuation coefficient k, for example 0.3 or more is required. However, any material for organic anti-reflective coatings satisfying such an attenuation coefficient k have been little known.
Under such circumstances, it is demanded to develop organic anti-reflective coatings efficiently absorbing reflection light from base substrate and thereby having an excellent anti-reflective effect.
Further, photoresists for lithography process for which irradiation light from F2 excimer laser are used are actively examined at present, and therefore it is considered that many kinds of photoresists will be developed in future. And, it is considered that a method of changing attenuation coefficient so as to suit required characteristics of each photoresist, for example a method of changing attenuation coefficient k comes to be important.
In the meanwhile, it is known that anti-reflective coating compositions containing fluorine-containing polymer is applied to lithography technique with F2 excimer laser as light source (see, for example, Japanese Patent Laid-open Nos. 2002-236370 and 2002-198283).
The present invention relates to a composition for forming anti-reflective coating, which has a strong absorption of light at a short wavelength, particularly light at wavelength of 157 nm. In addition, the present invention provides a composition for forming anti-reflective coating, which can be used in a lithography process for manufacturing a semiconductor device carried out by using irradiation light from F2 excimer laser (wavelength 157 nm). Further, the present invention provides an anti-reflective coating for lithography which effectively absorbs reflection light from a substrate when irradiation light from F2 excimer laser (wavelength 157 nm) is used for micro-processing, and which causes no intermixing with photoresist layer, and a composition for forming the anti-reflective coating. In addition, the present invention provides a method of forming an anti-reflective coating for lithography by using the composition for forming anti-reflective coating, and a method of forming a photoresist pattern. Further, the present invention provides a method of controlling attenuation coefficient k which is one of main characteristics of anti-reflective coating.